In the construction industry it is not uncommon to have many workers in the vicinity of a machine being operated to excavate, tunnel, bore, etc. For example, directional drills are commonly used to drill bores under obstacles such as waterways. In addition to the operator of the directional drill, workers are also needed to monitor and operate the "mud" system which is an integral part of many drilling operations. Workers are also needed at the exit hole to attach reamers, pipe casing, etc. to the end of the drill string before it is "pulled back" by the directional drill. In some operations, the workers located at the exit hole are a significant distance from the directional drill itself and may even be out of sight.
Under some circumstances, the workers at the exit hole would like to exert at least indirect control over the directional drill. Accordingly, it is common for workers at the exit hole to be in radio communication with the operator of the directional drill. The operator of the directional drill controls the drilling rig based on the voice commands he or she receives from the workers located at the exit hole.